More accustomed to tracking corruption in poorer African or Asian states, the organisation said links between the private and public sector favoured abuse of power, misappropriation and fraud, while also undermining economic stability.
A 60-page report titled "Money, politics and power: corruption risks in Europe" noted a strong correlation between corruption and fiscal deficits and said Greece, Italy, Portugal and Spain topped a list of nations found to have serious deficits in their integrity systems.
Of the 25 countries surveyed -- the European Union's 27 members minus Austria, Cyprus, Luxembourg and Malta, but including Norway and Switzerland -- only 19 regulate lobbies.
A mere 10 ban anonymous political donations.
"Across Europe many of the institutions that define a democracy and enable a country to stop corruption are weaker than often assumed," said Cobus de Swardt, who heads the watchdog.
A huge 74 per cent of Europeans believe corruption is a major problem in their country, according to EU surveys.
The report said many governments are not accountable enough for their public finances and contracts worth a whopping 1.8 trillion euros ($2.25 trillion) in the European Union each year.
Only two countries adequately protect whistleblowers from retaliation while 17 countries lack codes of conduct for parliamentarians.
Citizens seeking to access public information face barriers in 20 countries, Transparency International added.
Denmark, Norway and Sweden were the best protected, but there had been a serious roll-back on corruption in some central and eastern European countries -- notably the Czech Republic, Hungary and Slovakia -- since they joined the EU.